Connect TP-Link router to Internet

I have an old TP-Link router which is used as a Test network For VM's. The Network on the TP-Link has a different subnet mask (255.255.0.0) to my main network (255.255.255.0).

is they a way to give internet access to the TP-Link router.

Surely in the router there's the option to change the IP address of the device and the subnet mask. Go from there and you'll get everything working.

I cannot set a subnet mask of 255.255.0.0 on my router since it’s rubbish.

The TP-Link (test network) is simulating a network with a Subnet of 255.255.0.0 which means the servers cannot be moved to my main network ( /24 ) .